If-modified-since header?

Question

Google tells me I need to be hosted on a server that supports this header (and it makes sense from a Google perspective). My host tells me that his servers do support that header. Yet when I test my pages on his server, the tool I am using tells me no support. Can anyone here help me with this?

Answer 1

OK - for this to work, you need to insert a preamble on each PHP page -
<?php
$tsstring = gmdate('D, d M Y H:i:s ', $timestamp) . 'GMT';
$etag = $language . $timestamp;
$if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : false;
$if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? $_SERVER['HTTP_IF_NONE_MATCH'] : false;
if ((($if_none_match && $if_none_match == $etag) || (!$if_none_match)) &&
($if_modified_since && $if_modified_since == $tsstring))
header('HTTP/1.1 304 Not Modified');
exit();
else
header("Last-Modified: $tsstring");
?>
This is from the discussion here -
http://stackoverflow.com/questions/1971721/how-to-use-http-cache-headers-with-php
which I had seen once, but it was not clear to me that this was to be used on the pages involved, and thought it might be a way to check the if-modified-since header from a PHP page instead of a way to make the page send the header.